JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A08212,
doi:10.1029/2005JA011188, 2005
An obliquely propagating electromagnetic drift instability in the
lower hybrid frequency range
Hantao Ji and Russell Kulsrud
Center for Magnetic Self-Organization
in Laboratory and Astrophysical Plasmas, Plasma Physics Laboratory,
Princeton, New Jersey, USA
William Fox
Department of Physics, Massachusetts
Institute of Technology, Cambridge, Massachusettes, USA
Masaaki Yamada
Center for Magnetic Self-Organization
in Laboratory and Astrophysical Plasmas, Plasma Physics Laboratory,
Princeton, New Jersey, USA
Abstract
By employing a local two-fluid theory, we investigate an obliquely
propagating electromagnetic instability in the lower hybrid frequency
range driven by cross-field current or relative drifts between
electrons and ions. The theory self-consistently takes into account
local cross-field current and accompanying pressure gradients. It is
found that the instability is caused by reactive coupling between the
backward propagating whistler (fast) wave in the electron frame and the
forward propagating sound (slow) wave in the ion frame when the
relative drifts are large. The unstable waves we consider propagate
obliquely to the unperturbed magnetic field and have mixed polarization
with significant electromagnetic components. A physical picture of the
instability emerges in the limit of a large wave number characteristic
of the local approximation. The primary positive feedback mechanism is
based on reinforcement of initial electron density perturbations by
compression of electron fluid via induced Lorentz force. The resultant
waves are qualitatively consistent with the measured electromagnetic
fluctuations in reconnecting current sheet in a laboratory plasma.
Received 13 April 2005; accepted 7
June 2005; published 27 August 2005.
Keywords: current-driven microinstability; lower-hybrid drift
instability; electromagnetic waves; Whistler waves; magnetic
reconnection; anomalous resistivity.
Index Terms: 2772 Magnetospheric Physics: Plasma waves and
instabilities (2471); 2723 Magnetospheric Physics: Magnetic
reconnection (7526, 7835); 7827 Space Plasma Physics: Kinetic and MHD
theory; 7867 Space Plasma Physics: Wave/particle interactions (2483,
6984); 7835 Space Plasma Physics: Magnetic reconnection (2723, 7526).
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